refactoring Vertex and Edge hierachies by changing subclasses into instance variables of Vertex and Edge, this is done in preparation of the uml dot builder
added builder for dot format, added spec for build_entity of DotBuilder
renaming models directory to unit
added build_relation impl to DotBuilder, added spec for build_relation
removed scope declarations that were not needed
removed vertex factory
removing comments that arent needed
added uml builder and dot builder, added unit specs for both